1. Field of the Invention
The present invention relates to split system air conditioners and heat pumps. More specifically, the field of the invention is that of outdoor units for split system air conditioners and heat pumps.
2. Prior Art
Split system air conditioners and heat pumps are well known for heating and cooling residential and commercial buildings. The following examples describe conventional outdoor condensing units for air conditioners. Inside the building, an evaporator unit cools air circulated through the evaporator's refrigerant coils which contain circulating refrigerant fluid. Outside the building, the condenser unit dissipates heat into outdoor air passing through the condenser's refrigerant coils which also contain circulating refrigerant fluid. Lines for communication of refrigerant fluid connect the evaporator and condenser units to form a fluid circuit. Further, the air conditioner's compressor is conventionally disposed with the condenser unit outside the building, although the compressor may be disposed at any point provided it is in communication with the refrigerant fluid circuit. The above described arrangement may be switched by reversing a valve in the refrigerant fluid circuit so that the split system air conditioner acts as a heat pump to warm the indoor air and absorb heat from the outdoor air.
Condenser units for split system air conditioners are relatively larger than the condenser portions of room air conditioners, and are conventionally disposed on a concrete slab adjacent to the building with fluid lines connecting it to the compressor and the evaporator. In one conventional condenser unit configuration, one or more sides of the condensing unit include heat exchanger coils, and a large axial fan is positioned at the top of the condenser unit so that air is drawn through the heat exchanger coils and expelled out the top of the condenser unit. In another conventional condenser unit, an axial fan draws outdoor air through a side of the condenser, forces the outdoor air through a heat exchanger, and expels the outdoor air out the other side.
However, several disadvantages of conventional condenser units exist, particularly in terms of sound and efficiency. The condenser fans often produce an undesirable amount of noise. Often, condensing units are spaced away from the building to isolate this noise, away from the exterior wall boundary layer of outdoor air having ambient temperatures which are closer to the desired indoor temperature. This placement of condensing units outside and away from buildings also interferes with the landscaping around the building. Further, for apartments and condominiums, the condensing units take up scarce outdoor patio space.
The boundary air has lower (or higher during the heating season) ambient temperature because the sides of the building influence the outdoor boundary air by giving off or absorbing heat from the outdoor air. Under normal operating conditions, the building interior is closer to the desired indoor temperature than the outdoor air, and the temperature gradient from directly adjacent the building to several feet from the building may vary by up to 5.degree.. The condenser unit may be spaced away from the building and its boundary air, thus decreasing the efficiency of the air conditioner because it cannot take advantage of the temperature gradient from the boundary layer.
Another disadvantage of prior art condenser units involves the performance characteristics of axial fans. One important characteristic of a fan is its efficiency operating with heat exchangers having different pressure drops. Axial fans operate efficiently with heat exchangers having lower pressure drops. On the other hand, tangential or cross-flow fans can operate as efficiently with heat exchangers having higher pressure drops.
An advantage of cross-flow fans is that the fan extends across substantially the entire length of the heat exchanger coils, resulting in a more uniform airflow across the coils. This allows the cross-flow fan to operate at a higher speed, causing a greater air velocity and a higher heat transfer coefficient, and thereby requiring less heat exchanger surface area. Reducing the required heat exchanger surface area is desirable because that lowers the overall cost of the air conditioner.
However, conventional designs retrofitted with cross-flow fans do not possess the same operating efficiencies because a significant portion of the air passing through the cross-flow blower is recirculated within the condenser. Recirculating air impairs the efficiency of the condenser by lowering the temperature difference between the circulating refrigerant fluid and the air passing over the heat exchanger. Therefore, conventionally designed condenser units are not designed to effectively operate with cross-flow fans.
What is needed is a more efficient condenser unit for a split system air conditioner or heat pump.
Also needed is such a condenser unit which produces less noise.
Another need is for a condenser unit which occupies minimal outdoor space.
An additional need is for a condenser unit which may effectively operate with smaller heat exchangers.
A further need is for a condenser unit which effectively operates with cross-flow fans.